EVA Articles

Understanding Equine Viral Arteritis (EVA) AAEP Guidelines for breeding a mare to an equine arteritis virus-shedding

stallion

 

Understanding Equine Viral Arteritis (EVA)Equine Viral Arteritis (EVA) is a contagious disease caused by equine arteritis virus (EAV). While it is rarely life threatening to otherwise healthy adult horses, EVA is of special concern to horse breeders because it can cause abortion in pregnant mares, death in young foals and render breeding stallions permanent carriers of the virus.

Although EVA outbreaks occur infrequently, EAV is present in horse populations in many countries. While the virus is known to infect many breeds of horses, the prevalence of infection is much higher in certain breeds, most notably, Standardbreds and Warmbloods. This may be due to the high frequency of the carrier state in stallions of these breeds.

Clinical Signs

Most horses exposed to the virus will develop no signs of the disease. If illness does occur, EVA can be difficult to diagnose because it is clinically similar to several other equine diseases, such as Equine Rhinopneumonitis, influenza, Equine Infectious Anemia (EIA) and Purpura Hemorrhagica. The clinical signs vary in range and severity and can last from 2 to 14 days. They include:

Fever Swelling, most notably the legs, scrotum, sheath, mammary glands and above or around

the eyes Loss of appetite (anorexia) Depression Conjunctivitis - inflammation and discharge Nasal discharge Skin rash (frequently localized on the head and neck, but can be generalized) Abortion in pregnant mares Pneumonia and death in young foals Possible short-term subfertility in stallions that experienced significant fever and scrotal

edema

Diagnosis

The only definite means of diagnosing EVA is by laboratory testing. The virus can be detected in various tissues and fluids such as nasal or conjunctival secretions, semen, blood, placenta, fetal fluids and tissues. More commonly, the blood is screened for the presence of antibodies to the virus.

Collection of samples for testing should be instigated as soon as possible after the horse is noticed ill to increase the likelihood of confirming a diagnosis. Your veterinarian will know which laboratories are proficient in testing for EAV infection.

Transmission

EAV infection can be transmitted among horses in four different ways:

1. Respiratory: An acutely-infected horse spreads the virus to other in contact horses via respiratory secretions (exposure commonly occurs at racetracks, shows, sales and other events).

2. Venereal: Virus shed in the semen of an infected stallion is transmitted to mares when they are bred.

3. Indirect contamination: The virus is transferred indirectly through the use of contaminated tack or equipment shared among horses or on hands or clothing of personnel handling animals.

4. In utero: Virus passes across the placenta from an infected mare to her unborn foal.

Carrier State

Geldings, mares and sexually immature colts do not become persistently infected with EAV. Stallions infected with the virus may become permanent or long-term carriers. Even if a stallion never develops signs of disease, the virus may remain in his reproductive tract indefinitely. The virus is passed to the mares he is bred to – whether live-covered or artificially inseminated. A carrier stallion’s fertility does not appear to be adversely affected by persistence of the virus in the reproductive tract. Likewise, a stallion may have the virus in his serum and NOT in his reproductive tract. The best way to confirm your stallion’s status is by checking his blood status. If he is positive, you can try to isolate the virus in his semen to see if he is a risk for transmitting the virus venereally. It is generally accepted that if a stallion has the virus in his blood but NOT in his semen, he may be able to be bred safely. Mares that are being bred to a carrier stallion can also be vaccinated to protect them.

Currently, there is no fully proven therapeutic means of eliminating the virus from a carrier stallion’s reproductive tract. A small percentage of long-term carriers do, however, spontaneously clear the infection from their systems.

Prevention & Control

Sound management practices can help prevent and control EVA:

1. Isolate all new arrivals (and returning horses) to your farm or ranch for 3-4 weeks. 2. If possible, segregate pregnant mares from other horses. 3. Blood test all breeding stallions for EAV antibodies. 4. Check semen of any unvaccinated, antibody positive stallions to identify carriers before

breeding. 5. Vaccinate all breeding stallions annually. 6. Physically isolate any EAV carrier stallions. 7. Restrict breeding EAV carrier stallions to vaccinated mares or those whose blood is

positive for naturally-acquired antibodies to the virus. 8. Vaccinate mares against EVA at least 3 weeks prior to breeding to a known carrier

stallion. 9. Isolate mares vaccinated for the first time against EVA for 3 weeks following breeding to

an EAV carrier stallion (there is no need to revaccinate mares that need to be rebred). 10. In breeds or areas with high rates of EAV infection, it is recommended that all intact

males between 6-12 months of age be vaccinated as advised by your veterinarian.

If An Outbreak Occurs

In the event of an EVA outbreak, prompt action can prevent the disease from spreading and minimize its immediate and long-term economic impact. Follow these guidelines:

1. Isolate affected horses as soon as possible. 2. Notify your veterinarian immediately. 3. In consultation with your veterinarian, have the diagnosis of EVA confirmed by a qualified

laboratory. 4. If a mare has aborted, place the fetus and placenta in a leak-proof bag, refrigerate it and

send to the nearest appropriate laboratory for testing.

5. Disinfect the stall, equipment and facilities using a phenolic disinfectant as advised by your veterinarian. After treatment with disinfectant, dispose of bedding by composting in an area away from horses.

6. Wash down the mare’s hindquarters and tail with an antiseptic solution as advised by your veterinarian and keep her separated from other horses for at least 3 weeks.

7. Restrict the movement of all horses to and from the farm or ranch as advised by your veterinarian.

8. Suspend breeding operations until the outbreak is over. Notify mare owners. 9. Vaccinate all at-risk horses as advised by your veterinarian. 10. Notify your state veterinarian or appropriate state regulatory agency of the outbreak.

Immunization

Horses naturally infected with EAV develop a strong immunity against EVA, which can last for at least several years. Horses can also acquire immunity by being vaccinated against the disease.

Consult your veterinarian for information about an appropriate vaccination program to meet your individual needs. Vaccination should protect a horse against the disease for at least a year.

A blood test can confirm whether a horse has antibodies to the virus and the level of its immunity to this infection. This test cannot differentiate between a horse that is positive for antibodies to EAV as a result of vaccination or from natural exposure to the virus.

The EVA vaccine should be administered to stallions not less than 4 weeks prior to their use for breeding. There is no evidence that a vaccinated stallion will shed the virus in the semen or that the modified live virus vaccine against the disease can set up the carrier state.

A mare being vaccinated for the first time and bred to a carrier stallion should not be placed in contact with antibody negative horses for at least 3 weeks after her breeding date. While the vaccine will protect her from illness, she is almost certain to experience a limited re-infection cycle from the virus in the semen. During this time, she could serve as a source of infection for any unprotected horses through shedding virus via the respiratory route. This can have significant adverse consequences for pregnant mares and could result in an outbreak of abortion.

The modified live virus vaccine is not approved for use in pregnant mares nor in foals less than 6 weeks of age unless faced with a high risk of natural infection with EAV and only then if recommended by your veterinarian.

Positive Perspective On EVA

With the exception of very young foals, EVA is rarely fatal. Most horses that contract the disease make full, uneventful recoveries. Treatment, if implemented, is directed at reducing the severity of clinical signs during the course of illness.

If fever or swelling are severe, your veterinarian will likely prescribe non-steroidal and anti-inflammatory drugs to make the horse more comfortable. Horses should be able to return to work within 14-28 days.

With the help of your veterinarian, EVA should never be a problem. It is a very manageable infection. By implementing a sound vaccination and/or health care program, the risk of EVA can be minimized. For more information regarding EVA, contact your local veterinarian.

For more information, contact your veterinarian.

American Association of Equine Practitioners4075 Iron Works Parkway, Lexington, KY 40511(859) 233-0147

posted by Rose posted: 7/20/2005. Last updated: 7/20/2005

AAEP Guidelines for breeding a mare to an equine arteritis virus-shedding stallion

At least 30 days prior to breeding, the mare should be tested for serum neutralizing antibodies to equine arteritis virus. A blood sample should be submitted to a veterinary medical diagnostic laboratory approved by the USDA to conduct this serological test. Based on that result the following procedures are recommended.

ANTIBODY NEGATIVE (titer of less than 1:4 - Non-pregnant mares)

If the mare is found to be serologically negative, she should be vaccinated as soon as possible with the licensed modified live virus vaccine against EVA*. After vaccination, the mare should be isolated for 21 days to allow her time to develop adequate protective immunity against subsequent exposure to the virus and to prevent the minimal risk of spread of the vaccine virus to any susceptible horses with which she might come into contact. Twenty-one days following vaccination, the mare may be bred to a shedding stallion. She should not be bred to a shedding stallion during that period.

After being bred for the first time to a shedding stallion, the mare should be isolated for 21 days from any horses on the premises serologically negative for antibodies to the virus. Subsequent breedings do not require an additional period of isolation. Occasionally a mare may be vaccinated against EVA, but for some reason, is not bred that year to a shedding stallion. If this should happen, the mare should be vaccinated again before being bred to a shedding stallion. No isolation is necessary following re-vaccination.

ANTIBODY NEGATIVE (titer of less than 1:4) - Pregnant mares

The current licensed modified live virus vaccine against equine viral arteritis* is not approved for use in pregnant mares. While a mare that is in good health may be vaccinated following parturition, a mare that has had a complicated foaling, or is otherwise not in good health, should not be vaccinated until she has regained her health. The foal should also be in good health and be at least two weeks old before its dam is vaccinated.

There is minimal risk that suckling foals out of serologically negative mares may be exposed to the vaccine virus when the mare is vaccinated against EVA.

RE-VACCINATION

Mares that will be bred to shedding stallions should receive an annual booster vaccination against EVA 21 days prior to being used for breeding purposes. No isolation is necessary following re-vaccination.

ANTIBODY POSITIVE (titer of 1:4 or greater) - ALL MARES

Mares that test serologically positive for antibodies to equine arteritis virus can be bred to a shedding stallion without the need for prior vaccination against EVA. Antibody positive mares that are bred to a shedding stallion by natural cover should be kept separate from other susceptible horses for 24 hours to avoid possible mechanical transmission of virus from voided semen. Any vehicle used to transport such mares immediately following breeding to a shedding stallion should be thoroughly cleaned and disinfected prior to transport of susceptible horses.

Guidelines for breeding stallions

Prior to the breeding season (at least 60 days is recommended), the stallion should be blood tested for neutralizing antibodies to equine arteritis virus.

ANTIBODY NEGATIVE (titer of less than 1:4)

If serologically negative, the stallion should be vaccinated with a licensed modified live vaccine against EVA* and isolated for 30 days after vaccination. An annual booster vaccination against EVA should be given on a regular basis every 12 months but no sooner than 30 days prior to being used for breeding.

ANTIBODY POSITIVE (titer of 1:4 or greater)

If the stallion is found serologically positive for serum neutralizing antibodies to equine arteritis virus, without written evidence certifying his negative serological status prior to vaccination, he needs to be tested for presence of the carrier (shedding) state. This can be determined by either one of the following methods:

* Attempted isolation of equine arteritis virus from two separate ejaculates collected and submitted by an accredited veterinarian to a laboratory approved by the USDA to conduct this test; or

* Test breeding the stallion to two mares serologically negative for antibodies to equine arteritis virus at least twice on each of two consecutive days (four covers) and the mares checked for the development of serum antibodies to the virus 28 days after breeding.

ANTIBODY POSITIVE - NON SHEDDING STALLIONS

Serologically positive stallions with written certification of negative antibody status prior to vaccination against EVA by a USDA approved laboratory need not be tested for virus shedding.

Stallions serologically positive for antibodies to equine arteritis virus from natural exposure that have previously been tested and found to be non-shedders (non-carriers) of the virus should have written confirmation of their non-shedder status and receive an annual booster vaccination against EVA.

ANTIBODY POSITIVE - SHEDDING _STALLIONS

Shedding stallions can be used for commercial breeding provided they are managed in accordance with the above guidelines. Stallion owners and stallion managers should disclose the shedding status of their stallions to mare owners, breed associations and, where required, to state authorities. Shedding stallions can be safely bred to adequately immunized mares or to mares that have tested serologically positive for neutralizing antibodies to equine arteritis virus.

Occasionally, shedding stallions will spontaneously stop shedding equine arteritis virus. Owners may wish to retest the semen of shedding stallions from time to time to determine if the stallion is still shedding virus.

TEASER STALLIONS

Teaser stallions should be vaccinated against EVA on an annual basis in accordance with this protocol.

IDENTIFICATION OF CARRIER (SHEDDING) STALLIONS

It is recommended that breed associations publicly disclose the names of those stallions registered with their breed association that are confirmed shedders of equine arteritis virus.

PREVENTION OF THE CARRIER STATE

Breeding stallions that are found serologically negative for antibodies to equine arteritis virus should be vaccinated against EVA to prevent development of the carrier state.

In order to prevent the carrier (shedding) state, especially in those breeds in which the infection is widely prevalent, as well as to prevent equine arteritis virus infection, colts under 270 days of age that are serologically negative for antibodies to equine arteritis virus should be vaccinated against EVA. Written certification of their negative serological status to equine arteritis virus should be obtained before vaccination.

USE OF MODIFIED LIVE VACCINE AGAINST EVA

It is essential to have written official certification of a horse’s negative serological status to equine arteritis virus prior to initial vaccination against this disease. Stallions and mares that will be bred to shedding stallions should receive an annual booster vaccination against equine arteritis virus prior to being used for breeding purposes.

American Association of Equine Practitioners4075 Iron Works PikeLexington, KY 40511

(606) 233-0147www.aaep.org

posted: 6/16/2002. Last updated: 7/7/2006